The "Not-Too-Talkative" EBCM

 

 

 

I stopped off at a shop on the way home to check out a 2003 GMC truck. The ABS light was on and with key ON, engine OFF, the scan tool (Tech 2) indicated no DTCs. However, thirty seconds after the engine started, the EBCM lost communication with the scan tool.

 

"If you turn the key OFF for about a minute, and then turn the key to ON, you get EBCM data. But half a minute into engine run time you lose all EBCM data."

 

"What about the other modules?" I asked.

 

"All the other modules communicate fine with the engine running except for the EBCM."

 

The technician checked the voltage lines at the EBCM. "The voltage is solid," he said. "I checked the EBCM ground. It looked good."

 

"Yeah, I know, I know--looks can be deceiving. Things aren't always what they appear to be. So, I did a voltage drop test of the EBCM ground. With the engine running, it was about .010 volts."

I know the readers can tell us if the voltage drop is acceptable.

"I removed the ground, cleaned it up anyway. It made no difference. I made the metal shiny. I even pulled the EBCM and cleaned the metal behind it.

"Wow," I said."

You have to ask yourself what is the difference between the EBCM ground and the other computer grounds. That is, you have to ask yourself that question IF you didn't thoroughly collect customer information during the initial interview. Get your notepad out and review.

"Does the vehicle have any add-on devices?"

"No."

"Does the vehicle have a work history?"

"Not really."

"Come on--just answer yes or no, please."

The truck was involved in a fender bender and came from the body shop.

What is different about the EBCM ground? It is the only module grounded to the frame. The other modules are grounded to sheet metal. You guessed it--when the body shop replaced the fender, they never reconnected the battery ground pigtail.

"Time to go," I said.

"Wait--I have another one to diagnose."

"Not tonight. This is Jack McGinnis, signing off.